I always take the prescription form in my bag with my passport. This has always been enough, with the medication kept in their labelled boxes and I dont put a weeks worth in my box as the tablets have to be in their correct labelled boxes, and they are usually in labelled silver foil holders within the boxes anywhere. Once I am through any customs I usually divide my tablets up and put some in a zipped section in my case, so that I have that backup either way, should the case or the bag be lost or stolen. That way I will have enough in an emergency. I am surprised at how many people dont carry their prescription with them, as different countries have different rules so that something acceptable here may not be in another country.
Just as a safeguard I have over many years made a clear list of important things, so passport number, travellers cheques numbers when we had those, insurance emergency number, my own doctors phone number , various phone numbers of people I might want to get hold of. These I keep two copies of. Again one zipped in my case, the other zipped in my handbag, or in a hotel kept in a safe if there is one. That way in any sort of an emergency I can access them quickly, and should you need them they are to hand. Of course I destroy them when I get home, so dont have any possibility of anyone making use of them.
While I think of it, I also have at home one of those green and white emergency tubs which were provided by the Lions. The idea is that you put all information about doctors name next of kin medication etc etc on a form and then put it in the tub and place the tub in the fridge. Then there is a little label you can put by the front door, so any paramedic or emergency person would know to check the fridge and all your information is there so this can save valuable time and ensure that they know what medication you are on etc. If you do not already have one of these I think they are very worth having - so long as you remember to update changes in phone numbers etc.